Frequency filters are utilized in many applications. One of the more prominent uses is in communication devices. For example, communication devices operating on a cellular network may have a relatively small specified frequency range on which to operate. A frequency filter may work to allow only those frequencies within the specified frequency range to pass through and may attenuate any frequencies outside of that range. The range of frequencies a frequency filter allows to pass through defines the passband of the frequency filter whereas those frequencies outside of that range are considered sideband frequencies.
Where a communication device only operates within a single specified frequency range, a single frequency filter may be sufficient; however, in many applications, a communication device may need to operate within two or more specified frequency ranges. Where a communication device may need to operate within two or more specified frequency ranges a frequency filter for each specified frequency range may be necessary. For example, it is not uncommon for cellular devices to contain 15 filters to operate on 15 different bands. Under the current state of the art, frequency filters are essentially limited to a single frequency range. Tunable filters may help in this, but the tuning range of a tunable filter is very limited. Tunable filters may be capable of small frequency adjustments to the passband through an electrical control signal, for example, however, the passband of current tunable frequency filters cannot be adjusted by more than about ten percent without experiencing severe degradation of the signal.